Something (ALSA or pulseaudio) changes sink volume upon bluetooth connect

Question

The problem

I am setting up a small linux computer (C.H.I.P.) to be a bluetooth receiver using pulseaudio. The device is headless so I would like to get a configuration that works on boot. Everything is good except when my phone connects to C.H.I.P. something always sets its sink volume to 0%.

How do I get Pulse/ALSA to leave the Master volume alone when pulseaudio sets up the sink-input? Or maybe pulse is to blame - I'm not sure.

Things I have tried

Removing module-*-restore from pulseaudio.
Setting flat-volumes to no
alsactl store
Adding a directive to system.pa and/or default.pa to make pulseaudio set the volume of that sink to 100%

If I'm running alsamixer while my phone connects I see the volume go from 100% to 0% around the following log line:

D: [pulseaudio] protocol-native.c: Client amixer changes volume of sink alsa_output.platform-1c22c00.codec.analog-stereo.

The set up

Bluez advertises as a media/sink device
Pulseaudio runs as a system-instance (yes, I know why this is bad)
It watches bluez for connections
When my phone connects PA sets up a loopback sink-input to the ALSA sink
ALSA promptly sets the volume to 0%. This happens every time my phone connects via bluetooth

All I have to do is run alsamixer and set the Master volume to 100%.

Much more information

Here's my message to pulseaudio-discuss (zero replies as of this writing).

The nearby debug log lines:

I: [pulseaudio] client.c: Created 26 "Native client (UNIX socket client)"
I: [pulseaudio] protocol-native.c: Client authenticated anonymously.
D: [pulseaudio] protocol-native.c: Protocol version: remote 29, local 29
D: [pulseaudio] protocol-native.c: SHM possible: no
D: [pulseaudio] protocol-native.c: Negotiated SHM: no
D: [pulseaudio] protocol-native.c: Client amixer changes volume of sink alsa_output.platform-1c22c00.codec.analog-stereo.
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Requested to rewind 524288 bytes.
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Limited to 18200 bytes.
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: before: 2275
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: after: 2275
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Rewound 18200 bytes.
D: [alsa-sink-CDC PCM Codec-0] sink.c: Processing rewind...
D: [alsa-sink-CDC PCM Codec-0] sink-input.c: Have to rewind 18200 bytes on render memblockq.
D: [alsa-sink-CDC PCM Codec-0] source.c: Processing rewind...
I: [pulseaudio] module-device-restore.c: Storing volume/mute for device+port sink:alsa_output.platform-1c22c00.codec.analog-stereo:analog-output.
I: [pulseaudio] client.c: Freed 26 "ALSA plug-in [amixer]"
I: [pulseaudio] protocol-native.c: Connection died.

The full connection debug.

D: [pulseaudio] bluez5-util.c: Properties changed in device /org/bluez/hci0/dev_1C_56_FE_9D_1B_0E
D: [pulseaudio] bluez4-util.c: dbus: interface=org.freedesktop.DBus.Properties, path=/org/bluez/hci0/dev_1C_56_FE_9D_1B_0E, member=PropertiesChanged
D: [pulseaudio] bluez5-util.c: Unknown interface org.freedesktop.DBus.Introspectable found, skipping
D: [pulseaudio] bluez5-util.c: Unknown interface org.bluez.MediaTransport1 found, skipping
D: [pulseaudio] bluez5-util.c: Unknown interface org.freedesktop.DBus.Properties found, skipping
D: [pulseaudio] bluez4-util.c: dbus: interface=org.freedesktop.DBus.ObjectManager, path=/, member=InterfacesAdded
D: [pulseaudio] bluez4-util.c: dbus: interface=org.bluez.MediaEndpoint1, path=/MediaEndpoint/A2DPSink, member=SetConfiguration
D: [pulseaudio] bluez5-util.c: dbus: path=/MediaEndpoint/A2DPSink, interface=org.bluez.MediaEndpoint1, member=SetConfiguration
D: [pulseaudio] bluez5-util.c: Transport /org/bluez/hci0/dev_1C_56_FE_9D_1B_0E/fd11 state changed from disconnected to idle
D: [pulseaudio] module-bluez5-discover.c: Loading module-bluez5-device path=/org/bluez/hci0/dev_1C_56_FE_9D_1B_0E
I: [pulseaudio] card.c: Created 4 "bluez_card.1C_56_FE_9D_1B_0E"
D: [pulseaudio] module-bluez5-device.c: Acquiring transport /org/bluez/hci0/dev_1C_56_FE_9D_1B_0E/fd11
I: [pulseaudio] bluez5-util.c: Failed optional acquire of unavailable transport /org/bluez/hci0/dev_1C_56_FE_9D_1B_0E/fd11
I: [pulseaudio] module-bluez5-device.c: SBC parameters: allocation=0, subbands=1, blocks=3, bitpool=2
D: [pulseaudio] module-device-restore.c: Database contains invalid data for key: source:bluez_source.1C_56_FE_9D_1B_0E:null
I: [pulseaudio] source.c: Created source 5 "bluez_source.1C_56_FE_9D_1B_0E" with sample spec s16le 2ch 44100Hz and channel map front-left,front-right
I: [pulseaudio] source.c:     bluetooth.protocol = "a2dp_source"
I: [pulseaudio] source.c:     device.description = "MotoG3"
I: [pulseaudio] source.c:     device.string = "1C:56:FE:9D:1B:0E"
I: [pulseaudio] source.c:     device.api = "bluez"
I: [pulseaudio] source.c:     device.class = "sound"
I: [pulseaudio] source.c:     device.bus = "bluetooth"
I: [pulseaudio] source.c:     device.form_factor = "phone"
I: [pulseaudio] source.c:     bluez.path = "/org/bluez/hci0/dev_1C_56_FE_9D_1B_0E"
I: [pulseaudio] source.c:     bluez.class = "0x5a020c"
I: [pulseaudio] source.c:     bluez.alias = "MotoG3"
I: [pulseaudio] source.c:     device.icon_name = "audio-card-bluetooth"
D: [bluetooth] module-bluez5-device.c: IO Thread starting up
D: [pulseaudio] module-suspend-on-idle.c: Source bluez_source.1C_56_FE_9D_1B_0E becomes idle, timeout in 5 seconds.
D: [pulseaudio] sink-input.c: Negotiated format: pcm, format.sample_format = "\"s16le\""  format.rate = "44100"  format.channels = "2" format.channel_map = "\"front-left,front-right\""
D: [pulseaudio] module-suspend-on-idle.c: Sink alsa_output.platform-1c22c00.codec.analog-stereo becomes busy, resuming.
D: [pulseaudio] sink.c: Suspend cause of sink alsa_output.platform-1c22c00.codec.analog-stereo is 0x0000, resuming
I: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Trying resume...
I: [alsa-sink-CDC PCM Codec-0] alsa-util.c: cannot disable ALSA period wakeups
D: [alsa-sink-CDC PCM Codec-0] alsa-util.c: Maximum hw buffer size is 1489 ms
D: [alsa-sink-CDC PCM Codec-0] alsa-util.c: Set buffer size first (to 65536 samples), period size second (to 8192 samples).
I: [alsa-sink-CDC PCM Codec-0] alsa-util.c: ALSA period wakeups were not disabled
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: hwbuf_unused=0
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: setting avail_min=64656
I: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Time scheduling watermark is 20.00ms
I: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Resumed successfully...
D: [pulseaudio] module-suspend-on-idle.c: Sink alsa_output.platform-1c22c00.codec.analog-stereo becomes idle, timeout in 5 seconds.
I: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Starting playback.
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Cutting sleep time for the initial iterations by half.
D: [pulseaudio] module-suspend-on-idle.c: Sink alsa_output.platform-1c22c00.codec.analog-stereo becomes idle, timeout in 5 seconds.
I: [pulseaudio] resampler.c: Resampler 'ffmpeg' cannot do variable rate, reverting to resampler 'auto'.
D: [pulseaudio] resampler.c: Resampler:
D: [pulseaudio] resampler.c:   rate 44100 -> 44000 (method speex-fixed-1)
D: [pulseaudio] resampler.c:   format s16le -> s32le (intermediate s16le)
D: [pulseaudio] resampler.c:   channels 2 -> 2 (resampling 2)
I: [pulseaudio] resampler.c: Choosing speex quality setting 1.
D: [pulseaudio] memblockq.c: memblockq requested: maxlength=33554432, tlength=0, base=8, prebuf=0, minreq=1 maxrewind=0
D: [pulseaudio] memblockq.c: memblockq sanitized: maxlength=33554432, tlength=33554432, base=8, prebuf=0, minreq=8 maxrewind=0
I: [pulseaudio] sink-input.c: Created input 3 "(null)" on alsa_output.platform-1c22c00.codec.analog-stereo with sample spec s16le 2ch 44100Hz and channel map front-left,front-right
I: [pulseaudio] sink-input.c:     media.role = "music"
I: [pulseaudio] sink-input.c:     module-stream-restore.id = "sink-input-by-media-role:music"
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Cutting sleep time for the initial iterations by half.
D: [pulseaudio] module-stream-restore.c: Not restoring device for stream source-output-by-media-role:abstract, because already set
D: [pulseaudio] source-output.c: Negotiated format: pcm, format.sample_format = "\"s16le\""  format.rate = "44100"  format.channels = "2"  format.channel_map = "\"front-left,front-right\""
D: [pulseaudio] module-suspend-on-idle.c: Source bluez_source.1C_56_FE_9D_1B_0E becomes busy, resuming.
D: [pulseaudio] module-suspend-on-idle.c: Source bluez_source.1C_56_FE_9D_1B_0E becomes idle, timeout in 5 seconds.
D: [pulseaudio] memblockq.c: memblockq requested: maxlength=33554432, tlength=0, base=4, prebuf=0, minreq=1 maxrewind=0
D: [pulseaudio] memblockq.c: memblockq sanitized: maxlength=33554432, tlength=33554432, base=4, prebuf=0, minreq=4 maxrewind=0
I: [pulseaudio] source-output.c: Created output 3 "(null)" on bluez_source.1C_56_FE_9D_1B_0E with sample spec s16le 2ch 44100Hz and channel map front-left,front-right
I: [pulseaudio] source-output.c:     media.role = "abstract"
I: [pulseaudio] source-output.c:     module-stream-restore.id = "source-output-by-media-role:abstract"
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Cutting sleep time for the initial iterations by half.
D: [pulseaudio] memblockq.c: memblockq requested: maxlength=16777216, tlength=16777216, base=4, prebuf=0, minreq=0 maxrewind=0
D: [pulseaudio] memblockq.c: memblockq sanitized: maxlength=16777216, tlength=16777216, base=4, prebuf=0, minreq=4 maxrewind=0
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Cutting sleep time for the initial iterations by half.
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Latency set to 66.67ms
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: hwbuf_unused=500824
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: setting avail_min=64657
I: [alsa-sink-CDC PCM Codec-0] module-loopback.c: Max request changed
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Requesting rewind due to latency change.
I: [alsa-sink-CDC PCM Codec-0] module-loopback.c: Max request changed
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Requested to rewind 524288 bytes.
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Limited to 518560 bytes.
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: before: 64820
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: after: 64820
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Rewound 518560 bytes.
D: [alsa-sink-CDC PCM Codec-0] sink.c: Processing rewind...
D: [alsa-sink-CDC PCM Codec-0] sink-input.c: Have to rewind 518560 bytes on render memblockq.
D: [alsa-sink-CDC PCM Codec-0] source.c: Processing rewind...
I: [bluetooth] module-loopback.c: Skipping 0 bytes
D: [pulseaudio] module-suspend-on-idle.c: Source bluez_source.1C_56_FE_9D_1B_0E becomes busy, resuming.
D: [pulseaudio] core-subscribe.c: Dropped redundant event due to change event.
I: [pulseaudio] module.c: Loaded "module-loopback" (index: #22; argument: "source="bluez_source.1C_56_FE_9D_1B_0E" source_dont_move="true" sink_input_properties="media.role=music"").
I: [pulseaudio] module.c: Loaded "module-bluez5-device" (index: #21; argument: "path=/org/bluez/hci0/dev_1C_56_FE_9D_1B_0E").
D: [pulseaudio] bluez5-util.c: Transport /org/bluez/hci0/dev_1C_56_FE_9D_1B_0E/fd11 available for profile a2dp_source
D: [pulseaudio] bluez5-util.c: Unknown interface org.freedesktop.DBus.Introspectable found, skipping
D: [pulseaudio] bluez5-util.c: Unknown interface org.bluez.MediaPlayer1 found, skipping
D: [pulseaudio] bluez5-util.c: Unknown interface org.freedesktop.DBus.Properties found, skipping
D: [pulseaudio] bluez4-util.c: dbus: interface=org.freedesktop.DBus.ObjectManager, path=/, member=InterfacesAdded
D: [pulseaudio] bluez5-util.c: Properties changed in adapter /org/bluez/hci0
D: [pulseaudio] bluez4-util.c: dbus: interface=org.freedesktop.DBus.Properties, path=/org/bluez/hci0, member=PropertiesChanged
I: [pulseaudio] client.c: Created 25 "Native client (UNIX socket client)"
I: [pulseaudio] protocol-native.c: Client authenticated anonymously.
I: [pulseaudio] client.c: Freed 25 "Native client (UNIX socket client)"
I: [pulseaudio] protocol-native.c: Connection died.
I: [pulseaudio] client.c: Created 26 "Native client (UNIX socket client)"
I: [pulseaudio] protocol-native.c: Client authenticated anonymously.
D: [pulseaudio] protocol-native.c: Protocol version: remote 29, local 29
D: [pulseaudio] protocol-native.c: SHM possible: no
D: [pulseaudio] protocol-native.c: Negotiated SHM: no
D: [pulseaudio] protocol-native.c: Client amixer changes volume of sink alsa_output.platform-1c22c00.codec.analog-stereo.
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Requested to rewind 524288 bytes.
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Limited to 18200 bytes.
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: before: 2275
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: after: 2275
D: [alsa-sink-CDC PCM Codec-0] alsa-sink.c: Rewound 18200 bytes.
D: [alsa-sink-CDC PCM Codec-0] sink.c: Processing rewind...
D: [alsa-sink-CDC PCM Codec-0] sink-input.c: Have to rewind 18200 bytes on render memblockq.
D: [alsa-sink-CDC PCM Codec-0] source.c: Processing rewind...
I: [pulseaudio] module-device-restore.c: Storing volume/mute for device+port sink:alsa_output.platform-1c22c00.codec.analog-stereo:analog-output.
I: [pulseaudio] client.c: Freed 26 "ALSA plug-in [amixer]"
I: [pulseaudio] protocol-native.c: Connection died.
I: [pulseaudio] client.c: Created 27 "Native client (UNIX socket client)"
I: [pulseaudio] protocol-native.c: Client authenticated anonymously.
D: [pulseaudio] protocol-native.c: Protocol version: remote 29, local 29
D: [pulseaudio] protocol-native.c: SHM possible: no
D: [pulseaudio] protocol-native.c: Negotiated SHM: no
I: [pulseaudio] client.c: Freed 27 "ALSA plug-in [amixer]"
I: [pulseaudio] protocol-native.c: Connection died.
I: [pulseaudio] client.c: Created 28 "Native client (UNIX socket client)"
I: [pulseaudio] protocol-native.c: Client authenticated anonymously.
D: [pulseaudio] protocol-native.c: Protocol version: remote 29, local 29
D: [pulseaudio] protocol-native.c: SHM possible: no
D: [pulseaudio] protocol-native.c: Negotiated SHM: no
I: [pulseaudio] client.c: Freed 28 "pactl"
I: [pulseaudio] protocol-native.c: Connection died.

/etc/pulse/daemon.conf

daemonize = no
allow-module-loading = yes
allow-exit = no
use-pid-file = yes
system-instance = yes
high-priority = yes
realtime-scheduling = no
log-target = journal
resample-method = ffmpeg
enable-remixing = no
enable-lfe-remixing = no
flat-volumes = yes
default-sample-format = s32le
default-sample-rate = 44000
alternate-sample-rate = 192000
default-sample-channels = 2
default-fragments = 10
default-fragment-size-msec = 50

/etc/pulse/client.conf

extra-arguments = --log-target=syslog --system --disallow-exit -v

/etc/pulse/system.pa

.ifexists module-udev-detect.so
load-module module-udev-detect
.else
load-module module-detect
.endif
.ifexists module-esound-protocol-unix.so
load-module module-esound-protocol-unix auth-anonymous=1
.endif
load-module module-native-protocol-unix auth-anonymous=1
load-module module-stream-restore
load-module module-device-restore
load-module module-default-device-restore
load-module module-rescue-streams
load-module module-always-sink
load-module module-suspend-on-idle
load-module module-position-event-sounds
load-module module-bluetooth-discover
load-module module-bluetooth-policy
load-module module-switch-on-connect

/etc/pulse/default.pa

.nofail
.fail
load-module module-device-restore
load-module module-stream-restore
load-module module-card-restore
load-module module-augment-properties
load-module module-switch-on-port-available
.ifexists module-udev-detect.so
load-module module-udev-detect
.else
load-module module-detect
.endif
.ifexists module-jackdbus-detect.so
.nofail
load-module module-jackdbus-detect channels=2
.fail
.endif
.ifexists module-bluetooth-policy.so
load-module module-bluetooth-policy
.endif
.ifexists module-bluetooth-discover.so
load-module module-bluetooth-discover
.endif
.ifexists module-esound-protocol-unix.so
load-module module-esound-protocol-unix
.endif
load-module module-native-protocol-unix
.ifexists module-gconf.so
.nofail
load-module module-gconf
.fail
.endif
load-module module-default-device-restore
load-module module-rescue-streams
load-module module-always-sink
load-module module-intended-roles
load-module module-suspend-on-idle
.ifexists module-console-kit.so
load-module module-console-kit
.endif
.ifexists module-systemd-login.so
load-module module-systemd-login
.endif
load-module module-position-event-sounds
load-module module-role-cork
load-module module-filter-heuristics
load-module module-filter-apply

The sink-input that gets "muted".

0 ol-blue /etc/pulse # pactl list sink-inputs
Sink Input #0
    Driver: module-loopback.c
    Owner Module: 16
    Client: n/a
    Sink: 0
    Sample Specification: s16le 2ch 44100Hz
    Channel Map: front-left,front-right
    Format: pcm, format.sample_format = "\"s16le\""  format.rate = "44100" format.channels = "2"  format.channel_map = "\"front-left,front-right\""
    Corked: yes
    Mute: no
    Volume: front-left: 1 /   0% / -288.99 d,   front-right: 1 /   0% /
-288.99 d
            balance 0.00
    Buffer Latency: 0 usec
    Sink Latency: 0 usec
    Resample method: speex-fixed-1
    Properties:
        media.role = "music"
        module-stream-restore.id = "sink-input-by-media-role:music"
        media.name = "Loopback from MotoG3"
        media.icon_name = "audio-card-bluetooth"

The ALSA sink:

0 ol-blue /etc/pulse # pactl list sinks
Sink #0
    State: SUSPENDED
    Name: alsa_output.platform-1c22c00.codec.analog-stereo
    Description: sun4i-codec Analog Stereo
    Driver: module-alsa-card.c
    Sample Specification: s32le 2ch 44000Hz
    Channel Map: front-left,front-right
    Owner Module: 1
    Mute: no
    Volume: front-left: 1 /   0% / -288.99 d,   front-right: 1 /   0% / -288.99 d
            balance 0.00
    Base Volume: 65536 / 100% / 0.00 dB
    Monitor Source: alsa_output.platform-1c22c00.codec.analog-stereo.monitor
    Latency: 0 usec, configured 0 usec
    Flags: HARDWARE DECIBEL_VOLUME LATENCY
    Properties:
        alsa.resolution_bits = "24"
        device.api = "alsa"
        device.class = "sound"
        alsa.class = "generic"
        alsa.subclass = "generic-mix"
        alsa.name = ""
        alsa.id = "CDC PCM Codec-0"
        alsa.subdevice = "0"
        alsa.subdevice_name = "subdevice #0"
        alsa.device = "0"
        alsa.card = "0"
        alsa.card_name = "sun4i-codec"
        alsa.long_card_name = "sun4i-codec"
        alsa.driver_name = "sun4i_codec"
        device.bus_path = "platform-1c22c00.codec"
        sysfs.path = "/devices/platform/soc at 01c00000 /1c22c00.codec/sound/card0"
        device.string = "hw:0"
        device.buffering.buffer_size = "524288"
        device.buffering.fragment_size = "65536"
        device.access_mode = "mmap+timer"
        device.profile.name = "analog-stereo"
        device.profile.description = "Analog Stereo"
        device.description = "sun4i-codec Analog Stereo"
        module-udev-detect.discovered = "1"
        device.icon_name = "audio-card"
    Ports:
        analog-output: Analog Output (priority: 9900)
    Active Port: analog-output
    Formats:
        pcm

Why do you think it's a problem with ALSA? Pulseaudio's module-device-restore attempts to restore volumes, and calls amixer. Now whatever arguments it gives amixer don't seem to work out, because amixer understands them as a request to set volume to 0. So what happens if you use amixer manually to set the volume? Sometimes ALSA "quantifies" volume settings, and rounds them to the nearest values the hardware supports. Does this happen here? Then the problem could be that module-device-restore uses e.g. 99% instead of 100%, and ALSA rounds down. — dirkt, Jan 26 '17 at 08:05
One thing to try is to disable module-device-restore in the pulseaudio configuration files, and see if there's still an attempt to change the volume on connection. — dirkt, Jan 26 '17 at 08:10
@dirkt: I'm not sure what is to blame really. amixer correctly sets volume at any %. Giving amixer 0dB errors, but doesn't change the Master volume. — Dean Brundage, Jan 26 '17 at 16:21
@dirkt: I removed module-device-restore and the behavior does not change. See the "Things I've Tried" section of my question. — Dean Brundage, Jan 26 '17 at 16:21

score 1 · Answer 1 · answered Jun 15 '22 at 01:17

I believe the PulseAudio Bluetooth a2dp profile handling issue I investigated is the same. Namely that the media role volume is handled differently for the same pulseaudio item than the same item with another media role.

Here Bluetooth a2dp_source set the media role to music and it turns out that the sink-input volume was set to zero when the loopback module sink was created. The workaround was to set the sink-input to not zero once and it then stayed at this value.

I set the application volume with the gnome control center, its "Volume Levels" has volume control for each application, ie one that had no label was set to 0%, I set it to 100% and now the sound is always set to 100% when I connect the Bluetooth device. Issue fixed.

Note that I was able to reproduce the no volume issue with native Pulseaudio (without Bluetooth): PULSE_PROP='media.role=music' paplay <wave file> while a random media role was fine: PULSE_PROP='media.role=blob' paplay <wave file>. I was also able to fix it from gnome-control-center sound 'Volume Levels'.

Also it could requires this pactl fixup: How to reduce the volume of a background music stream when a different audio source is playing?

There is a documented CLI for changing per-client volumes... E.g., pactl set-sink-input-volume 1384 100%, where 1384 is the client number. The secret is that they're called "sink-inputs" for playback clients (and source-outputs for recording clients).

ie one can set the sink-input volume to 100% with: pactl set-sink-input-volume 350 100% and back to 0% with: pactl set-sink-input-volume 350 0% where 350 is the sink-input index.

What is weird is that the pactl sink-input-volume and gnome-control-center application volume level fixes re orthogonal. If one is 0% no sound.

Though I am pretty confident I fixed my Bluetooth loopback with gnome-control-center, my sink-input volume was initially 0%. My tests with paplay must have confused the debug process. But after the fact I can confirm that both application level and sink-input volumes requires to be upped.